The conventional wireless local area network standard enhances the support for quality of service (Quality of Service, QoS). The transmission opportunity (Transmission Opportunity, TXOP) in a hybrid coordination function (Hybrid Coordination Function, HCF) mechanism is a basic unit for radio channel access. The TXOP is a bounded period defined by the initial time and the duration, and allows continuous use of a channel within the duration. The duration cannot exceed the maximum duration (TXOP Limit).
In a basic service set (Basic Service Set, BSS) formed of an access point (Access Point, AP) and multiple stations (Stations, STAs), the AP and the STAs contend for a TXOP through a channel access process. Once the AP or a STA obtains the TXOP, the AP or the STA can continuously use the channel within the TXOP duration without contending for the channel again. Because within one TXOP, not all STAs need to receive data frames, so a very high throughput (Very High Throughput, VHT) TXOP power save mode (VHT TXOP power save mode) is introduced. When the STA finds that no data frame is sent to it, the STA enters the doze (Doze) state to save power during the TXOP. In the doze state, the STA can neither send data frames nor receive data frames, and thus the consumed power is very low. For a STA supporting TXOP power save (generally, a non AP VHT STA), if the AP in the current frame allows the STA in the BSS to enter the Doze state during the TXOP, the STA enters the Doze state when one of the following conditions is satisfied, and stays in the Doze state until the current TXOP ends:
(1) Through a group identifier (GROUP_ID) parameter in a receive parameter vector (RXVECTOR), the non AP VHT STA finds that the non AP VHT STA itself is not a member of the group.
(2) The non AP VHT STA finds that a partial association identifier (PARTIAL_AID) in the RXVECTOR is inconsistent with a partial AID of the non AP VHT STA, or the non AP VHT STA finds that the frame is not sent to the non AP VHT STA.
(3) Through the indication of the GROUP_ID parameter in the RXVECTOR, the non AP VHT STA finds that the non AP VHT STA itself is a member of the group, but the number of space-time streams (Number of Space-Time Streams, NUM_STS) in the RXVECTOR received by the non AP VHT STA is set to 0.
(4) The non AP VHT STA sends an acknowledgment signal to respond to the received frame whose More Data field is set to 0.
In the actual application process, the AP not only sends data frames to the STA, but also may require, through a null data packet announcement (Null Data Packet Announcement, NDPA) frame, the STA to feed back channel state information (Channel State Information, CSI). When the AP requires multiple rather than all STAs to feed back CSI information, by setting the GROUP_ID in the transmit parameter vector (TXVECTOR) of the NDPA frame to 63 and setting PARTIAL_AID to 0, the AP notifies all STAs by broadcast that the AP requires multiple STAs to feed back CSI information. In this case, none of the STAs satisfies any one of the conditions for entering the doze state. Therefore, all STAs are in the awake (Awake) state. Because the STAs are fully powered in the Awake state, a lot of power is consumed during the TXOP.